There are electronic devices in which a part or an entirety of an electronic component is covered with a resin molded body, and electronic devices in which an electronic component is fixed to a resin molded body without being coated with the resin molded body. Also, there are electronic devices having an electronic component, a first molded product made of a thermosetting resin that seals the electronic component, and a second molded product made of a thermoplastic resin which is secondarily molded outside of the first molded product.
As a method of manufacturing the electronic device having the resin molded body integrated with the electronic component, there is a method in which a first molded product is primarily molded with the thermosetting resin, and a second molded product to be joined to at least a part of the first molded product is secondarily molded with the thermoplastic resin. The electronic component is integrated with the first molded product.
The reason that the first molded product is molded with the thermosetting resin is because a linear expansion coefficient of the thermosetting resin is close to that of the electronic component, and the thermosetting resin is excellent in a sealing property for sealing the electronic component from the external. The reason that the second molded product is molded with the thermoplastic resin is because the thermosetting resin is high in the dimensional precision of the molded body, and high in toughness.
In the electronic device of this type, the first molded product made of the thermosetting resin is molded previously, and a curing reaction such as cross-linking or polymerization of the thermosetting resin has been completed. Therefore, when the second molded product made of the thermoplastic resin is secondarily molded on the first molded product, adhesion between the thermosetting resin and the thermoplastic resin is low, and peeling may occur therebetween.
Under the circumstances, there is a method in which after the secondary molding has been conducted, a gap between both the molded products is filled with a third resin as an inclusion. However, in this case, a work is required to fill the gap between both those molded products with the inclusion.
On the contrary, as disclosed in PTL 1, there has been proposed means for improving the adhesion in such a manner that the thermoplastic resin is allowed to be present on a surface of the first molded product of the thermosetting resin, and the respective thermoplastic resins are welded together at the time of secondary molding.
However, in the above PTL 1, it is necessary that a prepreg sheet and a thermoplastic resin (PA) film are laminated on each other, and subjected to heat press molding to obtain the first molded product having the thermoplastic resin on a surface thereof, which is not suitable as the means for sealing the electronic components from the viewpoint of component damage.
PTL 2 discloses a pressure sensor having a mold IC integrated with a sensor chip for pressure detection, and a connector case fixed with the mold IC. A mold resin of the mold IC is made of a thermosetting resin, and the connector case is made of a thermoplastic resin. In the pressure sensor, an interface between the mold resin and the connector case is covered with a potting material to prevent the ingress of gas or liquid, that is, to be sealed.
That is, because the thermoplastic resin used for secondary molding is low in adhesion relative to the thermosetting resin, a sealing material such as a potting material is applied to cover the interface between the first molded product and the second molded product after the molding of the second molded product for the purpose of sealing the interface between the first molded product and the second molded product.
However, in this case, a space for holding the applied sealing material must be ensured, or a groove or the like must be formed in the second molded product to prevent outflow of the applied sealing material. Thus, the shapes of the first and second molded products are restricted. Also, in reducing a size of the electronic device, it is preferable not to provide such a space. Therefore, it is desirable to achieve the sealing of the interface without applying the sealing material after the molding of the second molded product.
PTL 3 and PTL 4 disclose a photoresponsive compound that phase transitions from a solid phase or a liquid crystal phase to a liquid phase due to ultraviolet ray irradiation, and phase transitions to a phase before the ultraviolet ray irradiation due to visible light irradiation or heating, and also disclose that the photoresponsive compound is used as an adhesive. However, there is no disclosure of a specific method for achieving the sealing of an interface between the first molded product made of the thermosetting resin and the second molded product made of the thermoplastic resin.